Process of reacting cellulose fibers with carbonyl sulfide and product thereof



United States Patent 3 311,445 PROCESS OF REAC'liNG CELLULOSE FBERS WITH CAREONYL SULFIDE AND PRODUCT THEREOF Edward A. Swakon, Hammond, Ind, assignor to Standard Oil Company, Chicago, IiL, a corporation of Indiana No Drawing. Filed Dec. 6, 1963, Ser. No. 328,489 Claims. (Cl. 8-118) This invention relates to fibrous cellulosic material and more particularly pertains to novel modified fibrous cellulosic material and a method of preparing the same by a novel chemical method.

Cellulosic materials have been modified by converting cellulose into a xanthate with carbon disulfide and caustic soda and then regenerating the cellulose to form regenerated cellulose known as rayon.

Other cellulose regenerating processes for producing other types of rayons are known. Cellulose has also been modified by the formation of mono-, diand triesters thereof such as the acetates and these acetates formed into fibers, filaments and films. Cellulose acetate films have been further modified by either removing some of the ester moieties by hydrolysis and then reacting the reactive hydroxyl sites with chemical compounds other than the organic acids which undergo reaction with one or more cellulose molecules. Compounds which react with two or more cellulose molecules cause, of course, cross-linking. Other methods of modifying cellulose include mercerizing of cotton fabric or yarn. Mercerization involves the treatment of cotton fabric or yarn with strong caustic soda solutions at low temperatures, i.e. O to 35 C. For

the mercerization of cotton, caustic soda solutions ranging in strength from 19 to 38% caustic soda can be used. After the mercerization of cotton with caustic soda the yarn or fabric is passed through a mangle or squeeze rolls to remove the excess caustic and then washed with water with or without the application of tension to the yarn or fabric to prevent excessive shrinking before the mercerization of cotton can be modified by also Washing withdilute acid and water. In the mercerization process when the cotton has not been previously washed free from waxes and pectins, wetting agents are added to the aqueous caustic. In this case ordinary wetting agents cannot be used because they are not sufficiently solid and stable in concentrated caustic solutions and special wetting agents are used. However, those skilled in the art of mercerization are fully aware of the special wetting agents useful for the mercerization of cottons still containing waxes and pectins and only a 'few, such as those obtained from British cresylic acid, sulfonate-d ether acids of high molecular weight and dimethyl (hydroxyethyl) lauryl ammonium chloride, need be mentioned.

The method of this invention is a chemical modification of fibrous cellulosic material not at all the same as involved in preparing regenerated celluloses or the formation of cellulose esters or ethers or other processes which involve taking the cellulose into solution as a different chemical entity. Rather the method of this invention can be applied to fibrous cellulosic materials such as batts of cotton fibers and wood pulp among others. The method of this invention can also be employed with yarns, threads of cotton, woven cotton fabrics and even felted cotton fibers. The source of fibrous cellulosic material is not critical to the method of this invention and the fibrous celullosic material can be derived from wood pulp of hard or soft woods, cellulosic fibers from straw, jute, flax, bamboo, bagasse asparto, Sabai grass, hemp, ramie, fiber from. tree barks such as the paper mulberry and other natural sources of fibrous cellulose.

By the method of this invention articles of fibrous cellulosic material such as cotton yarns and thread can be ice so modified that they have the appearance of a monofilament and have in their modified form much greater strength than the original yarn or thread. Also by the method of this invention closely Woven cotton fabrics such as cheesecloth can be converted from the very soft fabric to a stifi, springy fabric resembling crinoline. Paper products can be modified by the method of this invention in such a manner that low quality white wood pulp paper is changed to appear as parchment paper, and very soft paper such as personal tissue paper is modified to a stiff paper having crackle and rather high resistance to tear.

Batts, mats and felts of fibrous cellulosic material can be so modified by the method of this invention to materials of much greater strength and having high resistance to shredding, snagging and the like.

The method of modifying fibrous cellulosic material of this invention comprises treating fibrous cellulosic material with aqueous solution of an alkali metal or alkaline earth metal hydroxide and then treating with carbonyl sulfide. Thereafter the fibrous cellulosic material so modified is washed with water and dried. The treatment with the aqueous solution of alkali metal or alkaline earth metal hydroxide can be accomplished by slurrying cellulosic fibers in the aqueous solution or by steeping prefabricated fibrous cellulosic materials such as yarns, threads, fabrics woven from said yarns or threads, mats, batts and felts of fibrous cellulosic materials in said alkaline aqueous solutions or by permitting said aqueous alkaline solutions to seepthrough said materials fabricated from fibrous cellulosic materials so that they are at least thoroughly wetted with said aqueous alkaline solutions.

The concentration of the aqueous solution of the hydroxides of alkali metals and alkaline earth metals is not critical to the method of this invention and can be varied from 1 to 70% by weight inclusive.

After treating the fibrous cellulosic material either in the form of fibers or fabricated materials, the fibrous cellulosic material is then treated with carbonyl sulfide either as a gas or a liquid. Since the reactivity of carbonyl sulfide with the base treated fibrous cellulosic material is rather slow at temperatures low enough to maintain carbonyl sulfide as a liquid, it is preferred, therefore, to carry out the carbonyl sulfide treatment with carbonyl sulfide vapors.

The method of this invention up to and through the treatment with carbonyl sulfide can be practiced with yarns, threads, woven fabrics, mats, batts, felts, by passing them through the aqueous solution of the hydroxides of alkali metals or alkaline earth metals and then through a chamber filled with carbonyl sulfide gas. There need not be imposed between the treatment with the basic aqueous solution and the carbonyl sulfide treatment the removal of excess basic aqueous solution, however, since the presence of excess basic aqueous solution may also react with carbonyl sulfide and, therefore, unnecessarily consume quantities of carbonyl sulfide, it is preferred to remove excess basic aqueous solution by draining or by pressing it out as with a mangle or with squeeze rolls.

After treatment with carbonyl sulfide the fibrous cellulosic matreial can be further treated by various means depending on the final properties desired. Some of these variations are:

(a) To water wash,

(b) To pass the material through a coupling or oxidizing solution such as dilute hydrogen peroxide, iodine or sodium hydrochlorite followed by water washing,

(c) To wash immediately with dilute acid such as sulfuric acid or acetic acid then followed by water washing,

(d) To age the carbonyl sulfide treated fibrous cellulosic material until at least some gelation has occurred on the surface thereof and then followed by water wash- (e) To hold the carbonyl sulfide treated material until gelation has occurred on the surface and then wash with dilute acid followed by water wash, and

(f) To further treat the carbonyl sulfide treated material with such chemical reactants as sodium monochloroacetate, ethylene oxide, chlorohydrin, phosgene and others then followed by water washing.

The treatment of the fibrous cellulosic material with the basic aqueous solutions can be carried out at ambient temperatures and even up to temperatures as much above normal ambient temperatures as 35 C. As hereinbefore stated the temperature of the treatment with basic aqueous solution is not critical and, therefore, temperatures above 35 C. can be used.

The method of this invention can be readily utilized by those who mercerize cotton yarn, thread, and fabrics by merely adding to the mercerization procedure treatment with carbonyl sulfide before Washing and/ or acid neutralization and Washing.

One theory for the modification of fibrous cellulosic materials by the method of this invention is that sodium monothiocarbonate groups are formed at least to a limited extent and then some form of regenerated cellulose forms upon treatment with water or dilute acid which cause cotton yarns and threads to appear as monofilaments and woven cotton fabrics to become stiff and springy by some bonding at the intersection even when a monofilament appearanoe does not occur. The same bonding at the intersection appears to occur to make a somewhat stronger final product from 'batts, mats and felts of cellulosic fibrous material. The bonding at the intersection can, of course, occur at the intersection of threads and yarns in woven fabrics or between intersections of individual fibers. However, the method of this invention does not rely for the utility thereof and the useful products that can be made thereby on said foregoing theories.

Through the use of the method of this invention molded articles can be manufactured which have a substantial permanent shape; for example hats can be made from cellulosic fibers such as wood pulp fibers, cotton linters, bagasse and other material cellulosic fibers without first forming the cellulosic fibers into a woven or plaiting such as braiding or interweaving of strands, strips or webbing. For example, cellulosic fibers such as cotton fiber, wood pulp fibers, cellulosic fibers from bagasse are slurried in a dilute caustic solution e.g. 2 to 15% sodium hydroxide at about 25 C. for 15 to 45 minutes. The resulting slurry is then deposited on a rotating perforated cone. Reduced pressure can be applied to the inner portion of the perforated cone to remove excess aqueous caustic solution. When a sufiicient thickness of the caustic treated cellulosic fibers is obtained the cone and the layer of caustic treated cellulosic fiber is placed in a chamber containing vaporized carbonyl sulfide. Carbonyl sulfide vapors are drawn through the layer of caustic treated fibrous cellulose and the unreacted carbonyl sulfide is returned to the chamber. The length of time of treating with carbonyl sulfide will, of course, vary with the thickness of the layer of caustic treated fibrous cellulose. The time of treating can be readily determined for various thicknesses and the final characteristic of the end product desired for thicknesses of about to about /s inch. The carbonyl sulfide treating time of about 5 to minutes will be adequate to give a firm end product. Thereafter the carbonyl sulfide treated cone of caustic treated fibrous cellulosic material can be considered much in the nature of a plastic preform and inserted into a die of the size and shape desired for the end product hat. The carbonyl sulfide treated product is preferably washed before further processing. Also by washing with dilute acid such as dilute sulfuric acid followed by water washing moisture resistance can be imparted to the final product. The washed carbonyl sulfide treated caustic steeped fibrous cellulose shape is heated to dry and form the hat. Temperatures of above 100 C. can be readily obtained by pressurized process steam and pressure on the mold members can be supplied in any desirable manner. After molding the hat can be treated in the usual manner.

-Dyeing of such molded articles of manufacture prepared in the manner described above can be accomplished before or after molding.

The method of this invention is illustrated by the following examples.

Example 1 Cotton fibers, 12.5 g., are steeped for one hour in 20% aqueous sodium hydroxide solution and then pressed to reduce the weight of the treated cotton to 58 g. The sodium hydroxide treated cellulose is shredded in a Waring Blendor and is then transferred to a 3-neck round bottom flask equipped with a stirrer, solid carbon dioxide cooled trap and a gas inlet. There is introduced into the flask 9 g. of carbonyl sulfide. As the carbonyl sulfide begins to react, the treated cotton becomes stringy and tangles around the shaft of the stirrer. The cotton material becomes greenish in color and rather stiff. Washing of the carbonyl sulfide treated cotton removes the green color and a white stiff product of tough strands are obtained. The individual fibers of the washed caustic- COS treated cotton appear to be fused together into a strong monofilament-like string. Cotton fibers, yarns or threads can be similarly treated to obtain a strong and stiff monofilament-like material.

Example 2 Chemical cotton (Hercules N301), 12.5 g., is steeped in aqueous 20% sodium hydroxide solution for one hour. Excess sodium hydroxide is squeezed out to obtain 30 g. of caustic treated cotton. This material is aged for 18 hours and is then reacted with 9 g. carbonyl sulfide for two hours. The reaction is exothermic on addition of carbonyl sulfide and the reaction vessel in which the carbonyl sulfide reaction is carried out is cooled with cold water. The carbonyl sulfide treated material takes on a gray meal-like appearance. The carbonyl sulfide modified chemical cotton is combined with 21 g. of aqueous 20% sodium hydroxide diluted with g. of water. The resulting mixture is thoroughly stirred. A product precipitates from the water. The precipitate is light gray, stringy, fibrous plastic in appearance. This product, after acidification with dilute sulfuric acid, is dried. The dried product has the appearance of fused plastic-like strings of fibers and retains the noted stiff and springy properties.

Example 3 A different chemical cotton (Hercules AZOOOP) is treated as described in the process of Example 2. The resulting product is much finer than that of the product of Example 2 for each particle appears to be fused. After washing the product of this method with water and dilute acid, a white-grayish, horny, tough material is obtained. This product no longer resembles the white, soft-textured cotton. Rather the cotton by the method of this invention is transformed into fused particles.

By either of the methods of Examples 2 or 3 cotton cloth or thread can be modified to produce a tougher product having low water absorbency.

Cotton can also be converted by the method of Examples 1 and 2 after longer contact with the caustic to a translucent film on the walls of the reaction flask during COS addition. The fihn can be peeled from the flask walls, removed from the flask and dried. By this method a White, stiff film is obtained. The dry, white (and opaque) film regains translucency upon wetting with water. The dry film is quite tough for its thickness in comparison with paper of the same thickness.

I Example 4 From 12.5 g. of chemical cotton (Hercules AZGOOP) there is prepared 30 g. of caustic treated material. This caustic treated material, in a manner hereinbefore described involving squeezing out of excess caustic, is then mixed with 95 g. ether. The mixture of caustic treated chemical cotton and ether is stirred and 8 g. of carbonyl sulfide is added over a period of one hour. Then 8 g. of aqueous 20% sodium hydroxide solution diluted with 95 g. water is added. A white, swollen, mushroom-like rubbery structure forms on the stirrer. The solid, rubbery material is removed from the stirrer and it is noted that the ether odor has disappeared from it. When a portion of this solid material is added to water it is found that water does not permeate the swollen structure. Another portion of the swollen structure upon acidification liberates gas and an expanded modified cellulose is obtained which retains its expanded structure even after drying.

Example 5 Five pieces of cheese cloth (about 0" square) are washed with ether and dried. Each ether-washed piece is treated in the following manner.

Piece I is washed with water. It is observed that after drying the ether and water-washed cheese cloth the resulting cloth is softer than the starting material probably because most of the stiffening material (size) has been removed.

Pieces II through V are each steeped in aqueous 20% sodium hydroxide solution for one hour and then squeezed to remove excess caustic solution. Thereafter, these pieces are treated as hereinafter described.

Piece II is washed with 2% sulfuric acid. The resulting cloth is white but has shrunk by about 33% has much smaller openings and is stiffer than Piece I. Piece III is placed in the tube and carbonyl sulfide is passed through the cloth for about one-half hour. Thereafter the carbonyl sulfide treated cloth is aged for about one hour and then added to 3.5 g. of aqueous 20% sodium hydroxide solution diluted with 16 g. water. The carbonyl sulfide treated cloth is held in this very dilute aqueous caustic solution for about 15 minutes, is removed, washed with water and dried. The cheese cloth so treated also shrink about 33% and is much stiffer than dried Piece II.

' Piece IV is treated with carbonyl sulfide in the same manner as described for Piece III. However, the aging after carbonyl sulfide treatment is for three hours. Thereafter the carbonyl sulfide treated Piece IV is washed with water and dried. Again it is found that the cheese cloth so treated shrinks by about 33%, but dry, treated Piece IV is bright white, stiff and springy resembling crinoline. Piece V is treated as described with respect to Piece III and is aged three hours. The carbonyl sulfide treated material is washed with 2% sulfuric acid, washed with water and is then dried. The dried, modified cheese cloth resists wetting when placed in water. The dry modified cheese cloth is not quite as stiff as Pieces II, III and IV.

There appears in Table I a weight of the pieces of cheese cloth in grams following the various treatments.

TABLE I.MODIFIED CHEESE CLOTH As the foregoing illustrated, cotton fabric no stronger than cheese cloth can be treated by the method of this invention to modify it from a soft material to a springy, stiff, crinoline-like material which will maintain its crinoline-like properties even after repeated washings. The retention of the new springy, stiff properties is provided by the partial fusing of individual strands of cotton. This also materially enhances the strength of the modified cotton fabric. Optimum stiffness is achieved by only water washing the carbonyl sulfide treated fabric (omitting washing with dilute acid) and then drying. It will be readily appreciated that by following the methods hereinbefore described, cotton fabric treated according to the method of this invention can be dried by the application of heat and pressure on a form of any desired shape and the dried product will retain the shape of the form.

Paper can be modified by the method of this invention to produce a new entity whose properties differ substantially from that of the starting paper. This is illustrated in Example 6.

Example 6 Five samples of soft personal tissue are steeped in aqueous 20% sodium hydroxide solution and then squeezed to remove excess caustic. Sample I is treated with 2% sulfuric acid solution and dried. Samples II through V are exposed to carbonyl sulfide for 40 min- TABLE II.MODIFIED TISSUE PAPER Sample: Properties of paper I Soft, easily fell apart, deteriorated.

II White, stiff, crackle, more resistance to tear. Ii Same as Sample II. IV Slightly poorer quality than Samples II and III.

V Same as Sample IV.

Of the above treated tissue paper, dried Samples II and III were the strongest, stiffest and most tear resistant. Dry Samples IV and V were slightly less strong, stiff and tear resistant. These results emphasize the advantages of applying the method of this invention to the treatment of paper; The method of Example 6 can be applied to the treatment of cardboard, strawboard, Kraft paper, bleached paper produced from wood pulp alone or in admixture with various cellulosic fiber rag content.

The method of this invention can also be applied to layers of paper-making fibers. For example, by seeping aqueous caustic solution through the wet web of the papermaking machine and thereafter passing the caustic treated wet web through a chamber containing carbonyl sulfide vapors and then drying the layer of paper-making fibers in the usual manner.

The method of this invention hereinbefore illustrated is a simple and inexpensive means of modifying and improving the chemical and physical properties of products such as paper cloth and thread fabricated from fibrous cellulosic materials. The method of this invention offers a means of surface coating treated cloth and paper through which fusion of at least some of the cellulosic fibers occurs and thus greatly strengthening the modified material as well as modifying the properties of the treated material with respect to changes in softness, elasticity and improving creasing or even crease resistance, adding water repellancy and heat resistance among other new properties. By the method of this invention fabricated articles from fibrous cellulosic materials can be transformed into plastic-like materials as for example cotton threads and yarns can be transformed into monofilamentlike products having greater strength than the original material. Also through the method of this invention two or more layers of paper or cloth, after treating with carbonyl sulfide, can be pressed or rolled together where by lamination, adhesion or cementation of the two materials can be made to occur. This joining of two or more layers is enhanced by heating the washed layers before subjecting them to pressing or rolling. Thus the method of this invention provides an entirely new field of surface coating cloth and paper and modifying materials fabricated from fibrous cellulosic materials.

By the method of this invention a new process for making felt-like fabrics is made possible. For example, layers of dry or wet cellulosic fibers such as fibers of cotton, wood pulp and the like are deposited as mats or batts, steeped in caustic solutions, squeezed, drained or treated in conventional ways to remove excess caustic solution after which the caustic treated cellulosic fibrous layer is treated with carbonyl sulfide, washed with or without aging and dried. As hereinbefore disclosed a wet mat of cellulosic fiber is deposited as in paper-making and then treated with an aqueous solution of the hereinbefore disclosed alkaline hydroxides or the mat can be deposited from a slurry of the cellulosic fibers in said aqueous alkaline solutions. After reaction with carbonyl sulfide the mat or batt can be reduced in thickness by passing through pressure rolls or pressed between plates to afford better fusing of the fibers after washing with water and/or dilute acid or merely by aging the mats and batts so treated by placing portions of the mats or batts so treated in heated molds under pressure to form articles of permanent shape.

An alternate procedure to the foregoing is to form a batt deposit of caustic treated cellulosic fibrous material and then treat the same with carbonyl sulfide followed by either aging, hydrolysis, acid neutralization, hydrogen peroxide coupling or chemical treatment with, for example, sodium chloroacetate, ethylene oxide, chlorohydrin, and anhydride of an organic acid, an organic acid halide or phosgene among others and finally washing the modified cellulosic fibrous material thoroughly.

A typical procedure for large scale utilization of the method of this invention would be to form a batt of cellulosic fibrous material by any of the conventional methods, conveying the batt into and through a bath of sodium hydroxide solution, then through means for removing excess caustic solution, then into and through a chamber containing carbonyl sulfide vapors, and then compressing the treated batt or mat to the desired thickness and width together with the aforementioned techniques of enhancing the fusing of fibers. The felt-like material is then thoroughly washed.

Example 7 illustrates the modification of batts of cellulosic fibrous material prepared according to the foregoing method.

Example 7 There is obtained 0.6 g. of cotton batting from a roll of surgical cotton. This cotton batt is washed with ether and dried. Thereafter the ether-washed and dried cotton batt is steeped in an aqueous solution containing sodium hydroxide for about one-half hour, removed from the aqueous solution and then pressed flat to a wet weight of 2 g. About one-third of the caustic treated cotton batt is cut off and set aside as a control sample. The remaining two-thirds of the caustic treated batt is placed in an Erlenmeyer flask, set in an ice bath and fitted with a condenser cooled with solid carbon dioxide. Carbonyl sulfide, 3 g., is introduced into the flask. The cotton batting turns yellow then light green upon introduction of carbonyl sulfide. The flask is sealed and carbonyl sulfide is permitted to reflux within the flask. After about 10 minutes the cotton batt becomes frosted. The cold trap is removed and the unreacted carbonyl sulfide is permitted to evaporate from the flask. The cotton batting thus t-reated is removed from the flask and out into three strips. One strip is placed in an aqueous solution containing 2% sodium hydroxide. This strip disintegrates into small fibers. The second strip is added to water and it is ebserved that it also disintegrat-es into small fibers. The third strip, after being permitted to age for about two weeks, changes in appearance for there are three translucent areas occupying about one-half of the area of the strip. In these translucent areas the fibers appear to be fused together, but the cotton batting remains soft. When the third cotton strip is then added to water it remains tightly bound, the translucent areas take on an opaque cotton whiteness. The fibers remain strongly bonded together. This aged water-washed third strip after drying remains white throughout and the fibers are strongly held together. The bonding of the fibers are strongest in the areas hereinbefore noted as translucent.

By following the method of Example 7 but permitting a longer contact time between the caustic treated cotton batting and carbonyl sulfide and a substantially shorter aging period, a soft, felt-like material can be obtained after washing the aged caustic treated and carbonyl sulfide reacted cotton Ibatting followed by drying. Such a cotton, felt-like material will have strong binding of fibers through the cotton, felt-like material. By partially compacting the caustic treated and carbonyl sulfide reacted, aged, Water-washed cotton batt between heated rolls or heated plates there can be obtained a stiffer, cotton, felt-like product. By exerting more pressure between heated rolls, heated plates or heated mold members a still thinner and stiffer product may be obtained. In any case the modified cotton felt-like product retains its bonding and shape permanently. Washing by conventional techniques does not remove the bonding.

A batt of wood pulp fibers laid down on a porous belt from a slurry of wood pulp fibers in dilute caustic is prepared. This continuous batt caustic treated wood fibers is passed through a chamber containing carbonyl sulfide vapors at about 2527 C. with a retention time in the carbonyl sulfide vapor chamber of about 10 to 20 minutes depending on the thickness of the caustic treated wood pulp fiber batt. Thereafter the carbonyl sulfide caustic treated wood pulp fiber :batt is aged for 15 to 45 minutes as it is carried on a porous belt supported on a series of rolls. After aging, the batt of aged caustic treated carbonyl sulfide reacted wood pulp fibers is washed with water and dried by placing between heated plates, exerting a slight pressure on the batt. The resulting dried batt is a wood pulp felt-like product.

In the above described process the washed, aged wood pulp batt is cut into shapes which, when placed in a mold having heated members shaped to form a box-like package and then dried under pressure, there is obtained thereby a packing box having a solid bottom and solid walls with apropriate Wall extensions to form the top closure of a packing box. Such a packing box when closed has a strength greater than a box fabricated from comparable thickness with corrugated strawboard and possesses water repellancy greater than conventional boxboard.

The foregin-g method permits the formation of fabrics from ibatts of cellulosic fibers eliminating the steps of combing, spinning and weaving. Not only does this provide a new route for such fabrics but also the method of this invention provides the manufacture of molded articles from cellulosic fibrous materials otherwise made by weaving, braiding, plaiting and the like. Furthermore, by the use of the process of this invention articles can be manufactured from cellulosic fibers unsuitable for spinning and weaving and which have not heretofore been useful in the manufacture of hats, mats, boxes, baskets, shoes and shaped packaging forms among other products.

The method of the foregoing examples can be carried out using aqueous solutions of potassium hydroxide, lithium hydroxide, calcium hydroxide or barium hydroxide in place of sodium hydroxide and substantially equal results obtained. The modification of cellulosic fibrous materials other than those illustrated can be accomplished by the method of this invention. a

What is claimed is:

1. A method of modifying fibrous cellulosic materials which comprises treating natural cellulose fibers with an aqueous solution of a hydroxide of a metal selected from the class consisting of alkali metals and alkaline earth metals to at least wet said fibers with said aqueous solution, thereafter reacting the cellulose fibers treated with said aqueous hydroxide solution with carbonyl sulfide without dissolving said fibers, and washing said carbonyl sulfide reacted cellulose fibers with water to obtain modified cellulose fibers.

2. The method of claim 1 wherein the metal hydroxide is sodium hydroxide.

3. The method of claim 1 wherein said natural cellulose fibers comprises cotton fibers.

4. The method of claim 2 wherein the natural cellulose fibers is paper.

5. The method of claim 2 wherein the natural cellulose fibers is cotton yarn.

6. The method of claim 2 wherein the natural cellulose fibers is a woven cotton fabric.

7. The method of claim 2 wherein the natural cellulose fibers is a mat of natural cellulose fibers.

8. A method of preparing a modified felt-like product from natural cellulose fibers which comprises slurrying natural cellulose fibers in an aqueous solution of sodium hydroxide, depositing a lbatt of cellulose fibers from said slurry, removing excess aqueous solution from said batt, thereafter reacting the wet batt with carbonyl sulfide, ageing said reacted fibers until at least some gelation 10 occurs on the surface of the batt fibers and after fiber bonding between the fibers of the batt has occurred washing said carbonyl sulfide treated batt with water and drying the water-washed batt.

9. A method of preparing a modified woven cotton fabric to impart stiffness and water repellancy thereto which comprises wetting said cotton fabric wth an aqueous solution of sodium hydroxide, reacting said wet fabric with carbonyl sulfide, ageing said carbonyl sulfide reacted fabric for several hours, washing said aged fabric with dilute acid and then with water, and then drying the resulting modified woven cotton fabric.

10. A modified natural cellulose fiber product obtained by the process of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2/1940 Givens et al 8-130 X 3/1961 Powers 8-130 X OTHER REFERENCES Chemical Abstracts, vol. 53, 1959, page 2613d, articleby Tyu-ganova et al.

NORMAN G. TO-RCHIN, Primary Examiner. H. WOLMAN, Assistant Examiner. 

1. A METHOD OF MODIFYING FIBROUS CELLULOSIC MATERIALS WHICH COMPRISES TREATING NATURAL CELLULOSE FIBERS WITH AN AQUEOUS SOLUTION OF A HYDROXIDE OF A METAL SELECTED FROM THE CLASS CONSISTING OF ALKALI METALS AND ALKALINE EARTH METALS TO AT LEAST WET SAID FIBERS WITH SAID AQUEOUS SOLUTION, THEREAFTER REACTING THE CELLULOSE FIBERS TREATED WITH SAID AQUEOUS HYDROXIDE SOLUTION WITH CARBONYL SULFIDE WITHOUT DISSOLVING SAID FIBERS, AND WASHING SAID CARBONYL SULFIDE REACTED CELLULOSE FIBERS WITH WATER TO OBTAIN MODIFIED CELLULOSE FIBERS.
 9. A METHOD OF PREPARING A MODIFIED WOVEN COTTON FABRIC TO IMPART STIFFNESS AND WATER REPELLANCY THERETO WHICH COMPRISES WETTING SAID COTTON FABRIC WTH AN AQUEOUS SOLUTION OF SODIUM HYDROXIDE, REACTING SAID WET FABRIC WITH CARBONYL SULFIDE, AGEING SAID CARBONYL SULFIDE REACTED FABRIC FOR SEVERAL HOURS, WASHING SAID AGED FABRIC WITH DILUTE ACID AND THEN WITH WATER, AND THEN DRYING THE RESULTING MODIFIED WOVEN COTTON FABRIC. 